I am a high school student and this is my research project for the IB and I basically want to know if it is possible to quantify the protein in (cow milk, almond milk, coconut milk, oat milk) and in case it is, do I need to dilute the milk? How should I do it? Can I get quantified results out of it? Can I do it with a CFL bulb?

It sounds like Warren answered the question. I can give some more background.

Proteins contain nitrogen, which isn't present in many other milk compounds. This nitrogen is often used to track the milk proteins. The earliest method I used was kjeldahl. Don't try this method unless you want to swear.

A number of other methods have been developed including some base on near infra-red NIR. Most of them are looking for casein.

Good luck with your project. Our district science fair is in late March.